OPTOEPIRET
Development of a exible epiretinal implant dummy with through-connections in the polyimide substrate
T.M. de Rijk (TU Delft - Mechanical Engineering)
P. J. French – Mentor
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Abstract
Millions of people suffer from retinal diseases worldwide. Retinal diseases can either be cured or treated. Retinal implants try to do the latter and aim to restore, partially, the vision in visually impaired people. This research thesis introduces a flexible implant with through-connections and a corresponding thinned silicon dummy chip that, when bonded together, could function as a base for a retinal implant. The project, named OPTOEPIRET, manufactures such a two-part epiretinal implant, which will be completely implanted inside the human eye.
The silicon chip has to be thinned in order to meet the flexibility properties needed due to the eye curvature. Different methods are discussed in this thesis. Thinning the complete wafer to 40 um and polishing the back surface before the chips are isolated yielded the best results. Eleven different versions of the polyimide substrate were fabricated. Ensuring the correct adhesion agents
are used for holding the gold pads into their corresponding polyimide holes was found to be critical. As well as ensuring a good connection between the gold pads and their corresponding paths.
The two parts are flip-chip bonded together and stress tested after the space between the two parts is filled with an underfill to spread the possible stress. The DC resistance was measured during bending of the dummy implant. Results showed the through-connections are able to withstand the bending stresses and forces during implantation into the human eye.